When we think about great hydrological engineering achievements, pride of place is normally given to familiar structures such as Hoover Dam, the California aqueduct, the Panama Canal, or less commonly to innovative examples such as the Falkirk Wheel (Figure 1). However, before we congratulate ourselves too profusely we should reflect on some truly astounding hydrologic achievements that were made thousands of years ago. Some of these ancient works were even more marvelous than our modern examples, particularly given the technology that was available in their day. It is best to reflect on this history before we launch into the subject of modern hydrology.